You get extra points in your suffer score for being "in the red" as far as your HR is concerned and so incorrect HR zones (i.e. too low) will affect it massively.
My last parkrun would have had a much higher suffer score as my HR was 10bpm higher than it usually is for the entire run (I had a bit of a cold but I felt like I put in the same effort as usual).
You get extra points in your suffer score for being "in the red" as far as your HR is concerned and so incorrect HR zones (i.e. too low) will affect it massively.
My last parkrun would have had a much higher suffer score as my HR was 10bpm higher than it usually is for the entire run (I had a bit of a cold but I felt like I put in the same effort as usual).